This invention relates in general to semiconductor devices and more particularly to tunnel diode type of semiconductor devices.
The tunnel diode is now a well known semiconductor device and conventionally consists of two regions of heavily doped semiconductor material of opposite conductivity types separated by a relatively thin junction which permits charge carriers to tunnel therethrough upon the application of a suitable operating potential to the semiconductor regions. More recently, a new tunnel diode has emerged in the form of a heterostructure and is typified in U.S. Pat. No. 4,198,644 entitled, "Tunnel Diode" issued to Leo Esaki on Apr. 15, 1980. The tunnel diode described in the Esaki patent is comprised of a heterostructure consisting of adjoining regions of GaSb.sub.1-y As.sub.y and In.sub.1-x Ga.sub.x As interfaced with a tunneling junction. This device, moreover, was noted to be fabricated by the process of molecular beam epitaxy which is a system adapted to provide ultra-thin, well defined multilayer heterostructures of high quality in a controlled manner. As such, atomically smooth surfaces and extremely sharp boundaries at the interface of two closely lattice matched semiconductors can be produced with a minimum number of defects. References describing the technique of molecular beam epitaxy (MBE) include the publications entitled:
"Structures Grown By Molecular Beam Epitaxy", L. L. Chang, et al., J. Vac. Sci, Technol., Vol. 10, No. 5, September/October, 1973, p. 655:
"Semiconductor Superfine Structures By Computer-Controlled Molecular Beam Epitaxy", L. Esaki, et al., Thin Solid Films, 36 (1976), pp. 285-298; and
"Molecular Beam Epitaxy (MBE) of In.sub.1-x Ga.sub.x As and GaSb.sub.1-y As.sub.y ", C. A. Chang, et al., Applied Physics Letters, Vol. 31, No. 11, Dec. 1977, pp. 759-761.
While the tunnel diode disclosed in the above mentioned Esaki patent is designed to operate with relatively lower doping levels than conventional tunnel diodes currently utilized, the present invention is directed to still a further improvement in such devices.
It is an object of the present invention, therefore, to provide a new and useful improvement in tunnel diodes requiring no heavy doping and which can be readily fabricated by the process of molecular beam epitaxy.